Aerosol cans for MDIs in particular pMDIs normally possess a bead. The bead allows a metering means, in particular a metering valve, to be attached to the can by crimping a ferrule skirt of the metering means around the bead. Generally the can has a neck near the open end of the can, and the wall between the neck and the open end of the can curves outwardly and then inwardly to provide the bead. The neck typically is a short region having a small diameter (typically the smallest diameter of the can) suitable to house an ‘O’ ring of circular cross section, while the lower portion of the bead facilitates positioning of the ‘O’ ring. The upper portion of the bead facilitates sealing of the metering means to the open end of the can. For example when a metering valve is sealed to the open end via a gasket seal, the desired formation of a face seal acting against the open end of the can is facilitated by the top portion of the bead. To form the bead requires an operation in which the neck and the curved wall between the neck and the open end of the can are formed in a workpiece during the processing of the workpiece into a finished can.
It is known to produce cylindrical metal aerosol cans for MDIs, in particular pMDIs from sheet metal (such as aluminium or aluminium alloy) in a transfer press by cutting a circular blank and forming the blank through a series of sequential operations to obtain an aerosol can having the desired form and size. Such operations typically include drawing, cutting, re-coning, curling and beading and optionally debossing. The known transfer presses have a reciprocable transfer slide for moving the workpieces through a series of in-line locations at which the operations are performed by appropriate tooling at each location.
FIG. 20 shows an arrangement for performing a beading operation on a workpiece 501 in such transfer presses. A mandrel 503 which is slightly smaller than the workpiece 501 is positioned within the workpiece 501 and a roller 505 is brought up to and positioned against the workpiece 501 urging it against the mandrel 503 so as to form a bead in the workpiece 501 having the required shape.
Movement of the roller 505 is controlled by a linkage system generally indicated by reference numeral 507 to position the roller 505 with respect to the mandrel 503. The linkage system has arms 512,513 with respective pivots 504,506. The arms are linked by an adjustable rigid bar 510, and the movement of arm 513 is biased by a return spring 508. A rotatable drive shaft 509 for the transfer press is located under the transfer slide (not shown) and the linkage system 507 is operated by a cam 511 mounted on the drive shaft. The linkage system 507 extends from the underside of the transfer slide to the topside for moving the roller 505 towards and away from the mandrel 503 as the cam 511 rotates.
In use, the workpiece 501 is positioned to receive the mandrel 503 and the roller 505 is moved towards the mandrel 503 to clamp the workpiece 501 between co-operating profiles on the mandrel 503 and the roller 505 while the mandrel 503 and roller 505 rotate causing the workpiece 501 to be rolled between the mandrel 503 and the roller 505 to form the bead. Once the bead has been formed, the roller 505 is moved away from the mandrel 503 releasing the workpiece 501 so that the workpiece 501 can be separated from the mandrel 503 and moved to the next location.
The bead has to be accurately formed for subsequently attaching a valve to the finished can. The above-described linkage system 507 for the back and forth movement of the roller 505 is complicated and includes several elements pivotally connected to each other. As a result, the positioning of the roller 505 to form the bead can be affected by a number of factors affecting the set-up of the linkage system 507 which may result in beads being formed that are outside the tolerances required for attaching the valve. For example, temperature changes both in the ambient surroundings and caused by heat generated by operation of the press over a period of time can result in a change in dimensions of one or more of the elements due to thermal expansion/contraction that affects the set-up of the linkage system 507. Another factor potentially affecting the set-up of the linkage system 507 is wear in any of the pivotal connections of the linkage system. In addition, inaccuracies in positioning of the roller 505 may arise at least partially because drive gears for rotating the roller 505 are moved in and out of mesh during each rolling operation.
A further drawback of the known transfer presses is that only one workpiece is formed at each location and therefore while the press may perform different operations on several workpieces at the same time according to the position of the workpieces in the sequence of operations, there is a limit on the total number of workpieces that can be produced in a given period of time.